1. Field of the Invention
The invention relates to a cage for a thrust roller bearing.
2. Description of Related Art
A conventional cage for a thrust roller bearing (hereinafter, simply referred to as “thrust cage”) is described in, for example, Japanese Patent Application Publication No. 2008-202797 (JP 2008-202797 A). The thrust cage has a large-diameter annular portion, a small-diameter annular portion and a plurality of cage bars. The large-diameter annular portion and the small-diameter annular portion are concentric with each other, and are located on substantially the same plane. The cage bars connect the large-diameter annular portion and the small-diameter annular portion to each other. The cage bars are arranged at intervals in the circumferential direction of the small-diameter annular portion.
Each of the cage bars is bent into a generally U-shape in the axial direction of the small-diameter annular portion, as viewed in a section taken along the radial direction of the thrust cage. Further, all the cage bars are bent toward the same side in the axial direction of the small-diameter annular portion. In the above-described conventional thrust cage, the cage bars are bent into a generally U-shape, so that the thrust cage has an enhanced roller retaining capability.
However, because the cage bars of the above-described thrust cage are bent into a generally U-shape in the axial direction, the radial load bearing capacity of the above-described thrust cage is lower than that of a thrust cage having cage bars that are not bent. Therefore, there has been a demand that local deformation of the thrust cage, which is caused by holding the thrust cage between an inner ring and an outer ring, should be further suppressed, and the stiffness of the thrust cage against a radial compressive load should be enhanced.